The present invention relates to a pumping device for diphasic fluids i.e. fluids which, at the intake of the device, under the prevailing pressure and temperature conditions, are formed of a mixture of a liquid with a gas which is not dissolved in the liquid, the liquid being or not being gas-saturated.
Pumping a diphasic fluid, for example, but not exclusively, a diphasic oil effluent formed by a mixture of liquid and gas raises problems which become more difficult with increasing values of the volumetric gas-to-liquid ratio under the thermodynamic conditions prevailing in the diphasic fluid at the inlet of the pumping device.
With reference to the above the volumetric gas-to-liquid ratio, which is briefly referred to in the following as the "volumetric ratio", is defined as the ratio of the volume of fluid in the gaseous state to the volume of fluid in the liquid state, the value of this ratio depending on the thermodynamic conditions of the diphasic fluid.
Irrespective of the design of the pumps used (alternating, rotary pumps, or pumps with suction effect), good results are obtained for a zero value of the volumetric ratio, since the fluid is then equivalent to a monophasic liquid fluid. Such pumping devices can still be used as long as the operating conditions do not lead to phenomena which are likely to vaporise a large fraction of the gas dissolved in the liquid, or when the value of the volumetric ratio at the intake of the pump is at most equal to 0.2. Experience shows that, beyond this value, the efficiency of these devices decreases very rapidly, so that they can no longer be practically used.
In order to improve the operation of existing pumping devices, the gaseous phase can be separated from the liquid phase before the pumping operation, and each of these phases is then separately processed in distinct pumping circuits. The use of such separate pumping circuits is not always possible and in any event makes the pumping operations more difficult.
Therefore, an attempt has been made to develop pumping devices which are not only adapted to increase the overall energy of the pumped diphasic fluid, but are also capable of producing a diphasic fluid having a volumetric ratio at the outlet of the device of a lower value than that of the fluid at the inlet.
Thus several designs of impeller blades have been described, for example in U.S. Pat. Nos. 3,299,821 and 3,951,565 and in French Patent Applications No. 2,157,437 and 2,333,139.